Thin, low Arctic clouds played an important role in the massive 2012 Greenland ice melt

Clouds over the central Greenland Ice Sheet last July were "just right" for driving surface temperatures there above the melting point, according to a new study by scientists at NOAA and the Universities of Wisconsin, Idaho and Colorado.

http://www.noaanews.noaa.gov/stories2013/20130403_greenlandicemelt.htm